Mixed Anatase Research Articles

Fabrication of a New Dye-Sensitized Solar Cell Using CuO/TiO2 Nanocomposite Synthesized via an Electrochemical Technique

Various standard methods have previously been used for the synthesis of nanoparticles that produce unhealthy waste. They are also considered unsafe and expensive methods. An alternative technology is needed to synthesize nanoparticles that consume less energy and are more environmentally friendly. In this research, a CuO/TiO2 nanocomposite has been synthesized with a mole ratio of 1.5:1, which produces good energy and no environmental pollution using an easy and fast method (electrochemical). The morphology and structure of the nanocomposite were examined using TEM, FESEM, AFM, and FTIR. The particle size of the CuO/TiO2 nanocomposites was found to range between 10.52 and 88.10 nm, while optical properties were diagnosed using UV-visible spectroscopy since its measurements showed the amount of gap energy (3.08 eV). The structure of the nanocomposite was demonstrated using X-ray diffraction (XRD), where the mixed anatase and rutile phases were observed for TiO2, while the monoclinic (tenorite) phase was observed for CuO. Additionally, dye-sensitized solar cells (DSSCs) have been fabricated from CuO/TiO2 nanocomposite, which was synthesized by a new green method, and pigments (methylene blue as a chemical dye and chlorophyll as a natural dye). These DSSCs were characterized by their high ability to absorb ultraviolet energy, where the efficiency of energy conversion ɳ of ITO-CuO/TiO2 was approximately 2.62 and 3.87% with chlorophyll (a natural dye) and methylene blue (a chemical dye), respectively, where ɳ of ITO-CuO/TiO2 with methylene blue is the best.

Silver-Doped Titanium Oxide Layers for Improved Photocatalytic Activity and Antibacterial Properties of Titanium Implants.

Titanium has a long history of clinical use, but the naturally forming oxide is not ideal for bacterial resistance. Anodization processes can modify the crystallinity, surface topography, and surface chemistry of titanium oxides. Anatase, rutile, and mixed phase oxides are known to exhibit photocatalytic activity (PCA)-driven bacterial resistance under UVA irradiation. Silver additions are reported to enhance PCA and reduce bacterial attachment. This study investigated the effects of silver-doping additions to three established anodization processes. Silver doping showed no significant influence on oxide crystallinity, surface topography, or surface wettability. Oxides from a sulfuric acid anodization process exhibited significantly enhanced PCA after silver doping, but silver-doped oxides produced from phosphoric-acid-containing electrolytes did not. Staphylococcus aureus attachment was also assessed under dark and UVA-irradiated conditions on each oxide. Each oxide exhibited a photocatalytic antimicrobial effect as indicated by significantly decreased bacterial attachment under UVA irradiation compared to dark conditions. However, only the phosphorus-doped mixed anatase and rutile phase oxide exhibited an additional significant reduction in bacteria attachment under UVA irradiation as a result of silver doping. The antimicrobial success of this oxide was attributed to the combination of the mixed phase oxide and higher silver-doping uptake levels.

Synthesis of graphene nanosheets from coffee ground waste and its incorporation to mixed-phase TiO2 as photocatalyst in anthracene degradation

The increasing level of coffee consumption in Indonesia causes a significant amount of coffee ground waste as landfill, leading to serious environmental problems on account of phenol derivatives and acidic compounds as its constituents. Containing high carbon content, waste coffee ground is a favourable biomass candidate to be converted into carbon-based material, such as graphene nanosheet (GN). Having wide surface area, graphene derivatives can be used to modify surface of many materials, such as TiO2. The aim of this study is to synthesize graphene-modified TiO2 with a mixed anatase:rutile phase (9:1) and to analyse its photocatalytic activity towards the photodegradation of anthracene, in comparison with unmodified TiO2. UV-DRS analysis showed a significant decrease in the band gap of TiO2/GN-A (2.78 eV) compared with TiO2 (3.00 eV), leading to an increase in photocatalytic activity (Kt TiO2 = 7.26 × 10-4 min−1; Kt TiO2/GN-A = 3.43 × 10-3 min−1). All in all, the synthesized photocatalyst materials presented promising potential to be applied as photocatalysts in photodegradation of organic compounds.

Mixed phase anatase nanosheets/brookite nanorods TiO2 photocatalysts for enhanced gas phase CO2 photoreduction and H2 production

CO2 photoreduction and H2 photocatalytic production reactions have been studied on different TiO2 polymorphs (anatase and brookite) engineered with specific nanocrystal shape. Anatase TiO2 materials of nanosheet morphology and brookite TiO2 of nanorod morphology were developed via a hydrothermal synthesis process. Mixed-phase anatase/brookite TiO2 materials of the above extreme cases were also developed, controlling the phase composition. The materials were fully characterized by a variety of techniques including structural, morphological, textural and electronic properties characterization. N2 physisorption analysis and CO2 adsorption isotherms have shown that minimum amount of brookite phase (i.e. ca. 7 wt%) in the final material improved the textural properties and the CO2 uptake ability. Electron paramagnetic spectroscopy (EPR) provided evidences for improvements in the formation and availability of photogenerated electrons in the mixed-phase materials. CO2 photoreduction was increased by ca. 220% in the optimized mixed-phase anatase/brookite TiO2. Photocatalytic H2 production rates were also improved by ca. 140%. The results in the present study have shown that the TiO2 phase as well as the amount of each TiO2 polymorph plays vital role in photocatalytic efficiency and that the photocatalytic improvement depends greatly on the specific reactions. The new insights provided herein would be of interest for studied focusing on materials shape engineering and phase composition and their effect on activity.

Tailoring performance of hybrid supercapacitors by fluorine-rich block copolymer-derived carbon coated mixed-phase TiO2 nanoparticles

Hybrid supercapacitors can function as both batteries and supercapacitors owing to their high specific energy and capacitive power, respectively. Transition metal oxide-based electrodes exhibit a high theoretical specific capacitance, but their large-scale application in charge storage devices is limited by their low conductivity and electrical stability. To address this problem, we introduced a highly conductive carbon coating over mixed-phase titanium dioxide (C/TiO2) using a novel carbon-rich polyacrylonitrile block copolymer containing an active pentafluorophenyl acrylate ester block (PAN-b-PFPA). The LiFePO4 (LFP) positrode and C/TiO2 negatrode assembled hybrid LFP║C/TiO2 @ 800 supercapacitor exhibited a high specific capacitance of 227 F/g (current density of 1 A/g), power density of 500 W/kg, and energy density of 32 W h/kg. Importantly, higher specific capacitance (∼84%) and Coulombic efficiency (∼96%) were maintained over 5000 charge–discharge cycles. The improved performance of hybrid LFP║C/TiO2 @ 800 supercapacitor is attributable to (1) selectively mixed anatase–rutile TiO2 phases that led to additional Ti3+ oxidation state formation, (2) firm porous carbon coating resulting from the surface anchoring of PAN-b-PFPA copolymer, and (3) fluorine/sulfur impurities from pyrolysis residues. The carbon coating of transition metal oxides from the pyrolysis of PAN-b-PFPA copolymers can facilitate the large-scale development of energy storage materials.

Controlling Composite TiO2 Powder Characteristics in the Solid-State Synthesis of BaTiO3 Powders for Improved Sintering and Permittivity: A Comparative Study

In this study, the anatase–rutile phase fraction of TiO2, which would play a vital role in the solid-state synthesis of BaTiO3, was controlled to form a composite phase. The composite TiO2 was applied to a solid-state synthesis reaction, and the tetragonality, dielectric properties, and microstructure of the resulting BaTiO3 powders were analyzed under different synthesis conditions of TiO2. Furthermore, a comparative analysis of solid-state-synthesized BaTiO3 powders prepared using anatase, rutile, and mixed (anatase + rutile) TiO2 was performed to elucidate the mechanism of improvement in the sintering behavior and dielectric properties of the BaTiO3 powder synthesized using the composite TiO2. As a result of applying composite TiO2, BaTiO3 powder with excellent tetragonality was synthesized. In addition, it is effective in powder growth and the control of powder morphology, so sintering and dielectric properties can be improved at relatively low temperatures.

Effect of Temperature Sintering on Grain Growth and Optical Properties of TiO2 Nanoparticles

Titanium dioxide (TiO2) nanoparticles were prepared by the sol–gel method and the structural, morphological, and optical properties were investigated at different sintering temperatures of 500, 600, 700, 800, and 900°C. A tetragonal structure of anatase, mixed (anatase–rutile), and rutile phases are observed in the X-ray diffraction (XRD) analysis. Pure anatase phase formation occurred at 500°C, whereas anatase-to-rutile phase transformation began at 600°C, and reaching complete conversion to rutile at 800°C. The average crystallite size increased from 23 to 34 nm for anatase and 38 to 62 nm for the rutile when sintering temperature increased from 500 to 900°C. The scanning electron microscope (SEM) result presented the increase of grain size (25–100 nm) with increasing the sintering temperature. The Fourier transform infrared (FTIR) spectra demonstrated the presence of TiO2 vibrational bonds in all samples. The optical bandgaps of the sintered TiO2 nanoparticles decreased with rising sintering temperature. Photoluminescence spectra exhibited three characteristic peaks centered at 380, 450, and 550 nm. The emission intensity increased with increasing the sintering temperature. The Mie analysis was also studied to calculate scattering cross-section, forward scattering, and asymmetry for different grain sizes. The results showed that by increasing the nanoparticle diameters, the peaks of all spectra are redshifted for larger grain sizes and cross-section peaks shift to high values. In this study, the sintering temperature is observed to have a strong influence on crystalline phase transformation, microstructure, and optical properties of TiO2 nanoparticles. The TiO2 sample sintered at 900°C shows the best result to be used as luminescent material due to the low optical bandgap energy.

Development of maintenance-free coatings using composite titania and silica

Atmospheric conditions and the effect of pollutants on the frequently exposed glass furnishings like windows in constructions and windshield in automotive industries often require maintenance due to their extensive usage and heavy exposure. This demanded an additional coating on the conventional glass furnishings to free from the pollutants without additional cleaning cost. Hydrophilicity and hydrophobicity are properties of titania (TiO2) and silica (SiO2) dielectric materials, although when coated as a composite material, they exhibit a larger affinity for water than carbon contamination. Hence, the contamination adsorbed on the surface of the glass can be easily cleaned by water without help of any detergent or cleaning agents. In this work, we report the fabrication and analysis of three TiO2-SiO2 composite coatings (single coated 1C, double coated 2C and triple coated 3C) on glass substrates using the sol-gel spin coating technique. The coatings were subjected to X-ray diffraction (XRD) analysis, which revealed a broad peak at Bragg angle 25 °, confirming the existence of mixed anatase TiO2 and amorphous SiO2. Fourier transform infrared transmission spectroscopy (FT-IR) studies on the coatings demonstrated peaks at 906 cm−1 and 768 cm-1 that corresponds to the characteristic bond of Si-O-Ti, and stretching bond of Ti-O-Ti respectively. The ultraviolet visible and near-infrared spectroscopy (UV-Vis-NIR) studies on the coatings endorsed 40% reflection in the ultraviolet and near-infrared spectral regions and found increasing the composite coating can increase the reflectance further. Finally, water contact angle (WCA) analysis indicated the hydrophilic character of the coatings, with contact angles of 74.8 ° (1C), 83.3 ° (2C), and 112.7 ° (3C) and suggested as a maintenance free coating on the glass furnishings.

Engineering of efficient visible light photocatalysts: Ti1–x+yCuxLayO2 (x = 0.03; y = 0, 0.005, 0.01) compositions

In dye-photocatalysis, widening the wavelengths absorption range of catalysts as well as aborting the recombination of the photoexcited charge carriers (electrons–holes pairs) are of paramount significance. In the current study, we report the photocatalytic characteristics of four compositions composed of TiO2, Ti0.97Cu0.03O2, Ti0.965Cu0.03La0.005O2 and Ti0.96Cu0.03La0.01O2 powders for two harmful dyes (Congo red and methylene blue). The X-ray diffraction technique verified the configuration of mixed anatase and rutile phases in pure TiO2 and Ti0.97Cu0.03O2 powders while Ti0.965Cu0.03La0.005O2 and Ti0.96Cu0.03La0.01O2 powders possess anatase phase only. The changes of the band gap structure and dimensions of the unit cell volume of TiO2 confirm the substitution of Ti4+ sites by Cu2+ and La3+ ions. Remarkable widening of wavelengths absorption with formation of long absorption tails were found in TiO2 (3.13 eV) through insertion of La3+ plus Cu2+ ions. Ti0.965Cu0.03La0.005O2 and Ti0.96Cu0.03La0.01O2 samples exhibit a visible light band gap of 2.3 and 2.7 eV, respectively. Based on SEM images, incorporation of Cu2+ and La3+ ions influences the surface morphology of TiO2. The resulting Ti0.97Cu0.03O2, Ti0.965Cu0.03La0.005O2 and Ti0.96Cu0.03La0.01O2 powders present enhanced photocatalytic activity towards Congo red dye degradation compared to pure one under natural solar spectrum. The best Ti0.96Cu0.03La0.01O2 catalyst exhibits superior photocatalytic activity of 96% for 10 ppm CR dye in 20 min as well as above average photocatalytic efficiency of 63% for 30 ppm CR dye in 120 min. As well, it showed acceptable photodegradation activity of 52% for 30 ppm MB solution in 140 min of sunlight irradiation. The heightened photodegradation efficiency of Ti0.96Cu0.03La0.01O2 catalyst can be clarified in terms of higher charge carriers’ separation (Cu2+ + e– → Cu+, La3+ + e– → La2+), oxygen vacancies, full anatase phase structure as well as the wide range of visible light absorption.

A novel single-step anodization approach for pani-doping oxide surfaces to improve the photocatalytic activity of titanium implants

Crystalline titanium oxides have shown photocatalytic activity (PCA) and the formation of antibacterial reactive oxygen species (ROS) when stimulated with UV light. Polyaniline (PANI) is a conductive polymer that has shown antibacterial effects. Previously, titanium oxides have been PANI-doped using a multi-step approach. In the present study, we compared PANI-doped specimens produced with a two-step method (ACV), to PANI-doped specimens produced by a novel single-step direct anodization (AAn) method, and a control group of anodized un-doped specimens. The surface morphology, oxide crystallinity, surface elemental composition, surface roughness, surface wettability, oxide adhesion, corrosion resistance, PCA, and ROS generation of each oxide group were evaluated. All groups exhibited mixed anatase and rutile phase oxides. The AAn group revealed less anatase and rutile, but more PANI-surface coverage. The AAn group exhibited significantly increased PCA after 60 min of direct UVA illumination compared to the ACV group, despite containing lower amounts of anatase and rutile. The ACV and AAn groups showed significant increases in ROS production after 4 h UVA illumination while the control group showed similar ROS production. These findings suggested that PANI doping using the novel direct anodization technique significantly improved PCA even for oxides containing less crystallinity. The S. aureus attachment response to each oxide group was also compared under UVA pre-illumination, UVA direct illumination, and no illumination (dark) lighting conditions. Although no significant differences were shown in the bacterial response, both PANI-doped groups exhibited less average bacterial attachment compared to the control group. The response of MC3T3-E1 pre-osteoblast cells to each oxide group was evaluated using MTT and live/dead assays, and no evidence of cytotoxicity was found. Since many, if not most, titanium implant devices are routinely anodized as a part of the manufacturing processes, these study findings are applicable to a wide variety of implant applications.

Effective Removal of Methylene Blue by Surface Alteration of TiO2 with Ficus Carica Leaf Extract under Visible Light.

The present study describes the use of a leaf extract from Ficus carica as a source of natural antioxidants for the surface alteration of bulk titanium dioxide (TiO2) in two steps. First, the hydro-thermal treatment of the bulk TiO2 material was carried out and followed by thermal annealing at 300 °C for 3 h in air. The role of the leaf extract of Ficus carica on the performance of the bulk TiO2 material for the removal of methylene blue (MB) was also studied. Various analytical techniques such as powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) were used to explore the crystalline structure, morphology, and composition. The bulk TiO2 material after the leaf-extract treatment exhibited mixed anatase and rutile phases, a flower-like morphology, and Ti, O, and C were its main elements. The average crystallite size was also calculated, and the obtained values for the bulk TiO2 material, 18.11 nm, and the treated bulk TiO2 material with various amounts, 5, 10, and 15 mL, of leaf extract were 16.4, 13.16, and 10.29 nm respectively. Moreover, Fourier-transform infrared spectroscopy validated the typical metal–oxygen bonds and strengthened the XRD results. The bulk TiO2 material chemically treated with Ficus carica has shown outstanding activity towards the degradation of MB under sunlight. The 15 mL of Ficus carica extract significantly enhanced the photocatalytic activity of the bulk TiO2 material towards the degradation of MB. The dye degradation efficiency was found to be 98.8%, which was experimentally proven by the Fourier Transform Infrared spectroscopoyy (FTIR) analysis. The obtained performance of the bulk TiO2 material with Ficus carica revealed excellent surface modifying properties for poorly-performing photocatalysts towards the degradation of synthetic dyes when used in their pristine form. The presented approach suggests that Ficus carica could be of great interest for tuning the surface properties of materials, either in the form of nano-size or bulk-phase in a particular application.

Starch built TiO2 nanoarchitecture with mixed anatase and rutile phase for high energy density supercapacitor electrode

TiO2 nanoparticles are generally known to have low capacity and poor cycle life when used for supercapacitor electrodes. This work improved the overall energy storage ability of TiO2 nanoparticles by growing them on an activated starch template, which creates polyhydroxylated points that act as nucleation sites for stable nanoparticle growth. The calcined products were studied for phase changes using XRD, TEM, and Raman. Consequently, a balance between the anatase and rutile phase in the TiO2 nanoparticles led to the highest energy storage capacity. The calcination resulted in lowered crystallite sizes, and the activated starch template imparted surface oxygen groups that contributed to enhanced supercapacitive performances. In this work, the TiO2 synthesized on an activated starch template is referred to as A-TiO2, the TiO2 grown on un-activated starch was U-TiO2, while the reference TiO2 synthesized without a template was referred to as unsupported-TiO2. A-TiO2, which has 72% anatase and 28% rutile, had the best result and showed specific capacitance as high as 388 Fg−1, energy density as high as 194 Wh Kg−1, a power density of 4473 W Kg−1, ESR of 0.53 ohms, and retention capacity of 99% after 20,000 cycles.

P5 - Photocatalytic Activity and Antibacterial Behavior of Polyaniline-Doped Titanium Oxide Layers

The purpose of this study was to evaluate the effect of polyaniline doping of mixed anatase and rutile phase titanium oxide layers on the resulting photocatalytic activity (PCA) and antibacterial behavior. Commercially pure titanium grade 4 (CPTi) samples were divided into three groups: (1) anodized in 0.5 M sulfuric acid (control); (2) electropolymerized using cyclic voltammetry in a mixture of 0.5 M sulfuric acid and 0.25 M aniline after anodization in 0.5 M sulfuric acid (ACV); and (3) anodized in 0.5 M sulfuric acid and 0.25 M aniline (AAn). SEM, XRD, and water contact angles were used to evaluate the surface morphology, oxide layer crystallinity, and hydrophilicity of the oxide layers (n= 3). The PCA was determined through methylene blue (MB) degradation assay using 365 nm UVA illumination (n= 7). The antibacterial behavior was evaluated by assessing the reduction in percentage of S.aureus attachment under three UVA lighting conditions: (1) a pre-illumination group in which samples were irradiated under UVA light for one hour prior to bacteria exposure; (2) direct illumination group in which samples were irradiated for one hour after bacteria exposure; and (3) a no illumination group in which the samples were kept in the dark for one hour after bacteria exposure (n= 5). SEM confirmed the presence of polyaniline on AAN and ACV group surfaces. XRD confirmed the presence of anatase and rutile peaks for all groups with lower peak intensities for the AAn group. AAn, with an average contact angle of 29.7°, showed significantly higher hydrophilicity (p= 0.041) compared to the ACV and control groups with average contact angles of 46.4° and 47.9°, respectively. AAn showed significantly higher MB degradation at 60 minutes when compared to ACV (p= 0.034). Bacterial testing showed no significance differences between the three groups. However, an increased trend of bacterial attachment reduction was shown for the AAn and ACV groups, averaging 90.7% and 87.7%, compared to the control group, averaging 72.7%, under direct UVA illumination. Doping of polyaniline into the titanium oxide layer by direct anodization in sulfuric acid and aniline improves the hydrophilicity and photocatalytic activity of the titanium surfaces. Although polyaniline doped titanium oxide showed promising trends, no significant differences were shown in the antibacterial behaviors of the surfaces that were tested in this study. Additional studies using different concentration of aniline in the anodizing electrolyte are needed to attempt to improve photocatalytic activity and reduce bacterial attachment.

Synthesis and electron irradiation modification of anatase TiO2 with different morphologies

Anatase TiO2 samples with three different morphologies were successfully prepared by the solvothermal method, and their photoelectric properties were tested. The mixed anatase TiO2 demonstrated the best photoelectrochemical water splitting performance with a photocurrent density of 0.84 mA/cm2 (1.23V vs. reversible hydrogen electrode (RHE)), carrier concentration of 1.29 × 1022 cm-3, and interface resistance of 29.20 Ω. Further, the anatase TiO2 samples with different morphologies were doped with nitrogen ions by electron beam irradiation in order to modify the defect concentration in these samples. Among them, the photocurrent density of mixed anatase TiO2 irradiated by 100 kGy obtained the highest current density at 0.99 mA/cm2 (1.23 V vs. RHE). Moreover, its carrier concentration reached 2.46 × 1022 cm-3 and interface resistance was reduced to 11.24 Ω. The photocatalytic properties of TiO2 with different morphologies and the effects of irradiation and nitrogen doping on the properties of the samples were investigated.

2D/2D Co-Al layered double hydroxide/TiO2 heterostructures for photoreduction of Cr (VI)

Co-Al layered double hydroxide (LDH)/TiO2heterostructures were synthesized using TiO2 nanobelts by a solvothermal method. X-ray diffraction analysis and morphology observation indicate that layered Co-Al LDH was grown on TiO2nanobelts consisted of anatase and TiO2(B). The phase composition of TiO2nanobelt samples depended on the calcined temperature. The phase composition of TiO2 affected the adsorption ability of composite samples. The pseudo-second-order kinetics model fits for the Cr(VI) ions adsorption kinetics of LDH/TiO2 composite samples. In the case of dark condition, the Cr(VI) removal using composite sample (LT4) was about 45%.In contrast, the Cr(VI) removal of the sample reached up to 100% within 10 min under full solar spectrum irradiation. The excellent performance of the sample can be ascribed to the formation of CoAl-LDH/TiO2 heterostructures consisted of one-dimensional TiO2 nanostructure with mixed anatase and TiO2(B) phases and optimized LDH loading. This heterostructure revealed relatively high stability. The interface of two phases effectively hinders the recombination of photo-generated carriers. In addition, the presence of uniformly distributed CoAl-LDH improved the conductivity and light absorption of the composite sample.

Humidity sensing properties of spray deposited Fe doped TiO2 thin film

In the present work, ferrite (Fe) doped TiO2 thin films with different volume percentage (vol%) were synthesized using a spray pyrolysis technique. The effect of Fe doping on structural properties such as crystallite size, texture coefficient, microstrain, dislocation densities etc. were evaluated from the X ray diffratometry (XRD) data. XRD data revealed a polycrystalline anatase TiO2 phase for sample synthesized up to 2 vol% and mixed anatase and rutile crystalline phase for sample synthesized at 4 vol% Fe doped TiO2. The crystalline size was observed to decrease with increase in Fe dopant vol% and also other structural parameters changes with Fe dopant percentage. In the present work, electrical resistance was observed to decrease with a rise in Fe dopant vol% and temperature of the sample. Thermal properties like temperature coefficient of resistance and activation energy also showed strong correlation with Fe dopant vol%. Humidity sensing properties of the synthesized sample altered with a change in Fe dopant vol%. In the present paper, maximum sensitivity of about 88.7% for the sample synthesized with 2 vol% Fe doped TiO2 and also the lowest response and recovery time of about 52 and 3 s were reported for the same sample.

MXene Ti3C2Tx-Derived Nitrogen-Functionalized Heterophase TiO2 Homojunctions for Room-Temperature Trace Ammonia Gas Sensing.

In this work, MXene Ti3C2Tx-derived nitrogen-functionalized heterophase TiO2 homojunctions (N-MXene) were prepared via the urea-involved solvothermal treatment with varying reaction time as the sensing layer to detect trace NH3 gas at room temperature (20 °C). Compared with no signal for the pristine MXene counterpart, the 18 h-treated sensors (N-MXene-18) achieved a detection limit of 200 ppb with an inspiring response that was 7.3% better than the existing MXene-involved reports thus far. Also, decent repeatability, stability, and selectivity were demonstrated. It is noteworthy that the N-MXene-18 sensors delivered a stronger response, more sufficient recovery, and quicker response/recovery speeds under a humid environment than those under dry conditions, proving the significance of humidity. Furthermore, to suppress the effect of the fluctuation of humidity on NH3 sensing during the tests, a commercial waterproof polytetrafluoroethylene (PTFE) membrane was anchored onto the sensing layer, eventually bringing about humidity-independent features. Both nitrogen doping and TiO2 homojunctions constituted by mixed anatase and rutile phases were primarily responsible for the performance improvement with respect to pristine MXene. This work showcases the enormous potential of N-MXene materials in trace NH3 detection and offers an alternative strategy to realize both heteroatom doping and partial oxidation of MXene that is applicable in future optoelectronic devices.

Influence of α-Al2O3 Template and Process Parameters on Atomic Layer Deposition and Properties of Thin Films Containing High-Density TiO2 Phases

High-density phases of TiO2, such as rutile and high-pressure TiO2-II, have attracted interest as materials with high dielectric constant and refractive index values, while combinations of TiO2-II with anatase and rutile have been considered promising materials for catalytic applications. In this work, the atomic layer deposition of TiO2 on α-Al2O3 (0 0 0 1) (c-sapphire) was used to grow thin films containing different combinations of TiO2-II, anatase, and rutile, and to investigate the properties of the films. The results obtained demonstrate that in a temperature range of 300–400 °C, where transition from anatase to TiO2-II and rutile growth occurs in the films deposited on c-sapphire, the phase composition and other properties of a film depend significantly on the film thickness and ALD process time parameters. The changes in the phase composition, related to formation of the TiO2-II phase, caused an increase in the density and refractive index, minor narrowing of the optical bandgap, and an increase in the hardness of the films deposited on c-sapphire at TG ≥ 400 °C. These properties, together with high catalytic efficiency of mixed TiO2-II and anatase phases, as reported earlier, make the films promising for application in various functional coatings.

Characterization of Pure Rutile Titania Nanoparticle Prepared by Feasible Method for Coatings and Visible Light-Driven Dye Removal Application

The pure phase of rutile titanium dioxide or titania (R-TiO2) was prepared by means of a strong acidic sol–gel process followed by treatment using a hydrothermal method. The as-prepared titania nanoparticles existed purely in the rutile phase instead of the mixed anatase phase of the respective titania (R-TiO2). The optimized reaction condition and precursor usage were the critical parameters for the formation of the particle size and uniform crystallinity of the rutile phase of TiO2 nanoparticle fabrication. XRD (X-ray diffraction), and Raman spectroscopic techniques were utilized to confirm the formation of the pure rutile phase of titania. SEM (scanning electron microscope) and TEM (Transmission electron microscope) images showed the cauliflower-like morphology of the as-prepared R-TiO2; reduced particle sizes of below 5 nm were observed and confirmed through high resolution images. The catalytic activity of the as-prepared R-TiO2 was tested under visible light irradiation for methylene blue dye degradation reactions. Dye degradation occurred very effectively, even at higher concentrations of methylene blue (MB), at reduced time intervals from 5 to 3 h of reaction time. The as-prepared rutile phase of pure titania nanoparticles was applied in a catalysis application for the purpose of inducing various types of organic dye degradation or catalytic transformation in the presence of visible light.

Study of phase composition, photocatalytic activity, and photoluminescence of TiO2 with Eu additive produced by the extraction-pyrolytic method

Due to the unique properties and wide array of applications of nanocrystalline materials based on titanium dioxide, the study of new synthesis approaches remains relevant. In this study, within the framework of the extraction-pyrolytic method (EPM), we suggest using the mixtures of Ti- and Eu-containing organic extracts based on valeric acid as precursors for fabrication of nanocrystalline TiO2-based powders with different Eu content: 0.5 mol%, 5 mol%, and 50 mol%. The thermal behavior of individual metal-containing extracts and their mixture was studied by thermogravimetric analysis and differential scanning calorimetry (TGA–DSC). To characterize phase composition and morphology of produced materials, the X-ray diffraction (XRD) method and scanning electron microscopy (SEM) were used. Photoluminescence properties of Eu3+ ions in TiO2 nanocrystals have been studied. Photocatalytic activity of produced materials was tested in the reaction of methylene blue (MB) oxidation under UV-VIS irradiation. Correlation between synthesis parameters (Eu content and pyrolysis temperature) and properties of produced materials (phase composition, photoluminescence and photocatalytic properties) has been studied. It was demonstrated that the presence of a Eu-containing extract in the precursor mixture increases the anatase-to-rutile phase transformation temperature. The highest efficiency (degradation degree of MB 96%) was shown by TiO2 powder consisting of mixed polymorphs, anatase (main phase) and rutile, with 0.5 mol% Eu additive. It was shown that anatase-to-rutile phase transformation in TiO2:Eu3+ nanoparticles manifests in a degradation of Eu3+ luminescence intensity.